General Information

Component Location





General Description

To control emissions and aid with fuel economy, heated oxygen sensors (HO2S) are mounted in the exhaust system. The front HO2S signal is used to control air/fuel ratio in closed loop fuel control while the rear HO2S is used to monitor the catalyst for proper operation. Because Oxygen sensors require a minimum temperature to operate properly a heater element is installed in the sensor. This reduces the warm-up time and ensures sensor performance during all driving conditions. The HO2S produces a voltage based on the oxygen content of the exhaust. A rich fuel mixture contains less oxygen than a lean mixture. With a rich mixture the HO2S will produce a higher voltage while a lower voltage will be produced with a leaner mixture.

DTC Description

If the sensor output is below 0.06 V under enable conditions, ECM sets DTC P0131.
(This DTC might be caused by the malfunction of Heater circuit, so, check the heater circuit first.)

DTC Detecting Condition





Diagnostic Circuit Diagram





Signal Waveform & Data




Fig. 1) Normal waveforms of front HO2S (the upper) and rear HO2S (the lower)
In closed loop operation the ECM monitors the HO2S signal. When the sensor voltage rises about.5V the ECM will command a leaner fuel mixture. As the exhaust from the leaner mixture reaches the HO2S the signal voltage will drop below.5V. At that point, the ECM will command a richer mixture which in turn will cause the sensor voltage to rise.